Since last fall, Toyota has recalled 6 million vehicles in the U.S. for problems involving sudden acceleration. The recalls started in September, when Toyota announced it was recalling and replacing floor mats on approximately 4.2 million vehicles which were allegedly causing accelerator pedals in the vehicles to become stuck in the depressed position, leading to uncontrollable and rapid acceleration of the vehicle. On January 21, Toyota recalled 2.3 million vehicles due to accelerator pedals on those vehicles becoming stuck in a depressed position, causing unexpected and unsafe acceleration.

Yesterday, the Los Angeles Times reported that some owners of Toyota vehicles that had undergone floor mat or accelerator pedal fixes had complained of continuing speed control issues. According to that report, the newly filed complaints claiming recurring sudden acceleration include incidents involving the Avalon, Camry and Matrix. Camry and Avalon models were included in both recalls, while Matrix were only part of the pedal recall. Reuters in now reporting that late-model Corollas – only included in the pedal recall – are also the subject of such complaints

According to the Los Angeles Times, the Avalon, Camry and Matrix, along with the Lexus IS and ES, are currently being given new brake override software as part of the recall fix. The brake override software is designed to automatically reduce the engine to idle when both the brake and the accelerator are depressed. The Times said some safety experts are concerned that the brake override software may in fact cause more problems by adding a new layer of software to the system.

The new recall fix complaints are also adding to fears that Toyota has yet to get to the bottom of the sudden acceleration problems. Some experts feel the vehicles’ electronic control system could be behind the problems, and Toyota has hired an independent consulting firm to examine the issue.

According to a Reuters report, NHTSA said there were no explanations as of yet for the small number of new complaints, but was moving quickly to address them.

David Strickland, the NHTSA administrator, said in a statement that the agency wants to “get to the bottom” of the matter and ensure that Toyota is doing “everything possible” to address the situation.

“If Toyota owners are still experiencing sudden acceleration incidents after taking their cars to the dealership, we want to know about it,” Strickland said.